I recently had a job involving a lot of punch in recording vocal dubs. When I do it the basic way - that is pressing Play, then Rec on punch in spot - the key is to start plenty in advance, since I don't want to miss the breath leading to the beginning note.
What I found myself missing was the ability to let the recording musician hear the few first notes of the previous recording - while at the same time recording the new overdub (plenty in advance).
And I really don't want to create a new track pr dub...

1 Set a short cut for "Time Selection: Set start point"
2 Right click rec button, choose "Recording mode: time selection auto punch"
3 Set the time selection very late
4 Begin recording.
5 Punch in with "Time Selection: Set start point"
6 Pull left side of the item to reveal all the recorded content and make a pretty transition.

The cool thing is you can just leave the time selection if doing more takes.
Also, punch out with "Time Selection: Set end point".

this is a nice workaround, but I'm sure there's another way I've seen described somewhere. previously, I've always messed around with multiple tracks, muting here and there and comping afterwards. not ideal.

When recording a voice or instrument, you may find that the optimal record level is a lot lower than the playback level you're aiming for in the mix, unless you're going to get a clipped, distorted signal.

So rather than record on your carefully nurtured vocal/guitar/bassoon track and then dial the take level up (every time!), or record hot and risk clipping, just:

- Record at the optimal level on a VST-lite *copy* of your playback track. -

Once recorded or comped, drag the new, optimal media item onto your carefully nurtured playback track, which is all ready with VSTs, envelopes, etc. Mute the record track, colour it purple. God it's so simple. Yes, it's bloody obvious, but others like me may have overlooked this method.

For each live recorded um, thing, I have a 'master' PLAY track which is not normally adjusted, and an identical, dispensable, 'RECORD' track (apart maybe from level, fewer VSTs and sends/receives) which can be named appropriately for daily/hourly/instantaneous takes. And of course it can be duplicated for alternate takes; but you never need to adjust the 'PLAY' track once you're set, or unless you're in tweak mode.

This may be common 1-0-1 practice that even the noobiest noob would know, but I didn't suss it till today. (Smacks forehead). Not just Reaper, but if it's easier in another DAW I'd be surprised. I'm trying to imagine how it would work with tape.

A good one if you don't know it: (shift +?) double-click on a selected mixer track (not the pan area) zooms that track (and toggles zoom) in the track window. A boon with multiple monitors, anyway, and eliminates most of that track height adjustment/locking.